1. Field of the Invention
This invention generally relates to projectors, and more particularly, to a projector capable of automatically adjusting images projected, and an auto-focusing method used in the projector.
2. Description of Related Art
Using a projector to beam a magnified image on a screen or the like is widely used in many situations such as presentations in businesses, schools, advertisements, and so on.
Conventionally, a manual-focusing method is used to obtain a clear image. A focal length and/or a position of a projection lens of a projector are adjusted manually according to different positions of the projector relative to the screen. This manual-focusing method is cumbersome and time-consuming.
An auto-focusing method was also proposed. In such a method, a photographic device, for example, a video camera, is used to perform an auto-focusing operation. FIG. 6 shows a video camera 907 being used as a projector 900. The projector 900 includes a projection lens 901, a light valve 902, a light source 903, a test pattern generating circuit 904, a microcomputer 905, an analog to digital (A/D) converter 906, an adjusting mechanism 908, a dichroic mirror 911, and a reflecting mirror 912.
The dichroic mirror 911 reflects a light beam emitted from the light source 903 to the light valve 902. The microcomputer 905 controls the test pattern generating circuit 904 to generate a test pattern on the light valve 902. According to the test pattern, the light valve 902 selectively transmits the inputted light beam. The portion of the inputted light beam that is passed through the light valve 902 is reflected by the reflecting mirror 912, and is sequentially converged to the screen 800 by the projection lens 901 to form a test image on the screen 800. The test image is photographed by the video camera 907. The photographed image is subjected to an A/D conversion by the A/D converter 906 and then the digitized image data are inputted to the microcomputer 905.
The microcomputer 905 compares parameters of the digitized image data with that of the test image data that are pre-installed in the microcomputer 905, including contrast ratio, brightness, and so on. The microcomputer 905 controls the adjusting mechanism 908 to adjust the focal length and/or position of the projection lens 901 based on the analysis results. After adjustment, the projector 900 is in an in-focus state, that is, the image projected onto the screen 800 is clear.
As described above, the projector 900 of the auto-focusing method further requires a video camera 907 to capture the test image projected on the screen 800. When the video camera 907 is oriented to the screen 800 in different directions, the captured test image will have different contrast ratio and brightness. This may cause problems and difficulties for the user to orient the video camera 907 towards the screen 800 correctly.